Method for ultrasonic inspection of irregular and variable shapes

ABSTRACT

System and method for enabling ultrasonic inspection of a variable and irregular shape. The system comprises one or more ultrasonic pulser/receivers, one or more ultrasonic transducer arrays, a shoe or jig to hold and position the array(s), data acquisition software to drive the array(s), and data analysis software to select a respective best return signal for each pixel to be displayed. This system starts with information about the general orientation of the array relative to the part and a general predicted part shape. More specific orientation of the transmitted ultrasound beams relative to the part surface is done electronically by phasing the elements in the array(s) to cover the expected (i.e., predicted) surface as well as the full range of part surface variability.

RELATED PATENT APPLICATION

This application is a divisional of and claims priority from U.S. patentapplication Ser. No. 13/532,815 filed on Jun. 26, 2012.

BACKGROUND

This disclosure generally relates to inspection equipment and methods,and deals more particularly with methods and apparatus for inspectingstructures having irregular and variable shapes, especially soft-tooledstructures made of composite material.

A variety of elongated composite structures may have relatively confinedinternal cavities that require inspection in order to assure that thestructure meets production and/or performance specifications.Conventional composite structure cured with hard tooling results incomposite radii that are well defined and repeatable. In contrast, thecomposite radii formed using soft tooling are not always well definedand may vary from part to part. In some cases, dimensional or contourvariations may be greater than those that would result from using hardtooling. These larger variations make reliable inspection usingconventional methods more challenging. In view of the deviation fromcircularity of soft-tooled composite radii, the term “radius” as usedhereinafter should be construed non-strictly to include non-circularprofiles.

Critical composite structure in aerospace and potentially inapplications outside aerospace must be inspected to requiredspecifications to ensure structural integrity. Inspecting soft-tooledcomposite structures presents distinct yet interrelated challenges.Critical inspection areas include the radii. Moreover, such soft-tooled“radii” must be inspected in a production environment. For a productioninspection, the inspection rate must be sufficient to meet the partproduction rate.

For ultrasonic inspection of composite structure, the ultrasound beamshould ideally enter at 90 degrees to the local surface of the compositepart being inspected. If it does not enter at 90 degrees, it will berefracted off normal and a return echo from any possible internalstructure or anomaly will not be optimum. Traditionally a 90-degreeentry angle is maintained by holding a sensor array at a precisely fixedposition in space relative to the surface. While this works well forknown surfaces, such as flat or cylindrical surfaces of a given, fixedradius and circular shape, this approach will not provide adequateresults for surfaces which are, for example, parabolic, irregular, or ofvarying radius of not necessarily cylindrical cross section. Traditionalmethods of interrogating such a radius with ultrasound fail to keep thesound path sufficiently perpendicular over the entire inspection area.

There is a need for methods and apparatus for inspecting compositestructures having internal cavities that allow inspection of soft-tooledradii from inside the cavity. The methods and apparatus must alsoprovide that the sensor energy enters the composite part volume veryclose to the local perpendicular at the inspection site.

SUMMARY

The system and method disclosed herein enables the ultrasonic inspectionof a variable and irregular shape. An example of a primary use of thisscanning system would be for the inspection of a variable radius or anoncircular radius produced using soft tooling to form a compositestructure, such as an integrally stiffened wing box of an aircraft. Thesystem comprises one or more ultrasonic pulser/receivers, one or moreultrasonic transducer arrays, a shoe or jig to hold and position thearray(s), ultrasonic data acquisition application software to drive thearray(s), and ultrasonic data acquisition application software to selectthe best signal for each pixel to be displayed.

The ultrasonic data acquisition/analysis system disclosed herein has theability to scan a part of variable and irregular shape starting with ageneral orientation of the array relative to the part and a generalpredicted part shape. More specific orientation of the transmittedultrasound beams relative to the part surface is done electronically byphasing the elements in the array(s) to cover the expected (i.e.,predicted) surface of the part as well as the full range of part surfacevariability. The phasing is done in accordance with predetermined focallaws. (As used herein, the term “focal laws” refers to the programmedpattern of time delays applied to pulsing and receiving from theindividual elements of a transducer array in order to steer and/or focusthe resulting ultrasound beam and echo response.) The ultrasonic dataanalysis application software then selects the best return signal foreach spatial element of the part for display as a pixel and discardsother return signals. The disclosed system is able to scan at a fastrate, mechanically simple and robust.

For one specific application involving the inspection of a soft-tooledradius of an integrally stiffened wing box, the above-describedultrasonic data acquisition/analysis system can be integrated into anon-destructive inspection system comprising: an active trailer vehiclethat carries the ultrasonic transducer array(s) for inspecting thesoft-tooled radius; an external motorized tractor used to move theactive trailer vehicle through the tunnels of the wing box; one or moreultrasonic pulser/receivers connected to the ultrasonic transducerarrays; a computer that hosts the ultrasonic analysis, data acquisitionand movement control software; and a monitor for displaying C-scanimages of the inspected part.

One or more computer programs, i.e., software, running on a computer orother hardware and software system with a processor capable of operatingunder software control, may be used for acquisition of ultrasonicinspection data by the ultrasonic transducer arrays connected to one ormore pulser/receiver devices, and related or combined software may alsobe used to analyze the received data. Data analysis software interpretsthe inspection data and maps a C-scan from the probe onto a displaymonitor for review by an operator, such as a technician performing ascanning operation. For example, the software may combine the inspectiondata from ultrasonic transducers with position data from an opticalencoder with predefined structural data representing the configurationof the structure under inspection, including any position informationfor discontinuities in the structure, to provide the technician avirtual image of the ongoing non-destructive inspection by theultrasonic inspection system. Data analysis software may also provide auser with tools for further controlled analysis of the displayed data.

In accordance with one aspect, a method for inspecting a portion of apart having a surface of unknown shape is provided which comprises: (a)electrically pulsing respective groups of transducer elements of anarray in accordance with respective focal laws of a first set of focallaws to emit a plurality of focused beams in sequence, the focused beamsbeing directed from different angles toward a target location on thesurface; (b) after each respective group of transducers is pulsed,receiving electrical signals from the respective group in accordancewith respective focal laws of a second set of focal laws to form arespective return signal representing a respective echo returned to arespective group from the inspected part; (c) processing the returnsignals to derive respective values of a parameter characterizing thereturn signals; and (d) selecting one of the respective parameter valuesthat satisfies a first condition. In one embodiment, the parameter canbe amplitude and the first condition is having the greatest amplitude.For such an embodiment, the method further comprises displaying a pixelhaving a value which is a function of at least the selected parametervalue.

In another embodiment, the method further comprises: selecting anotherof the respective parameter values that satisfies the first condition ora second condition; and displaying a pixel having a value which is afunction of at least the two selected parameter values. The methodfurther comprises supplying fluid acoustic couplant into a space betweenthe array and the part, wherein step (c) comprises applying respectivegains to the respective return signals, the gains being selected tocompensate for different amounts of energy loss caused by transmissioninefficiency at higher angles. The respective gains being a function ofdistance of travel of each echo through the fluid acoustic couplant.

In accordance with another aspect, a method for inspecting a portion ofa part having a surface of unknown shape is provided which comprises:(a) determining a shape of an inspection zone and a range of variationthereof; (b) determining a position of an ultrasonic transducer arraythat, when phased, can project focused beams at a plurality of targetlocations in the inspection zone; (c) determining focal laws forinterrogating target locations of inspection zones having shapes whichvary within the range of variation using focused beams having differentsteering angles; (d) positioning the ultrasonic transducer array in thedetermined position: (e) pulsing the ultrasonic transducer array inaccordance with the determined focal laws; (f) forming respective returnsignals representing respective echoes returned to the ultrasonictransducer array from the inspected part; and (g) selecting a respectiveparameter value of a respective best return signal for each interrogatedtarget location. The selected parameter values are then displayed aspixels on a display monitor.

In accordance with a further aspect, a method for inspecting a portionof a part having a surface of unknown shape is provided which comprises:(a) positioning an array of transducer elements at a position along anaxis with an orientation that allows the array, when phased, to projectfocused beams which are respectively normal or nearly normal to firstand second target locations on the surface, a centerline of the arrayand the first and second target locations lying in a first plane; (b)while the array is in the position along the axis, electrically pulsingrespective groups of transducer elements of the array in sequence usingtime delays in accordance with a first set of focal laws, which pulsingcauses each pulsed group to emit a respective focused beam directed atthe first target location at respective steering angles; (c) applyingtime delays in accordance with the first set of focal laws to formrespective return signals from electrical signals output by therespective groups of transducer elements in response to echoes from thefirst target location following emission of the focused beams directedat the first target location; (d) selecting a first return signal havinga characteristic which indicates it corresponds to an emitted beam thatwas normal or nearly normal to the part surface at the first targetlocation; (e) while the array is in the same position, electricallypulsing respective groups of transducer elements of the array insequence using time delays in accordance with a second set of focallaws, which pulsing causes each pulsed group to emit a respectivefocused beam directed at the second target location at respectivesteering angles; (f) applying time delays in accordance with the secondset of focal laws to form respective return signals from electricalsignals output by the respective groups of transducer elements inresponse to echoes from the second target location following emission ofthe focused beams directed at the second target location; (g) selectinga second return signal having a characteristic which indicates itcorresponds to an emitted beam that was normal or nearly normal to thepart surface at the second target location; and (h) displaying first andsecond pixels in a first column, wherein the first pixel has a valuewhich is a function of at least a parameter value of the first returnsignal, and the second pixel has a value which is a function of at leasta parameter value of the second return signal.

Yet another aspect is a method for inspecting a part having a surface,the method comprising: (a) positioning a first array of transducerelements at an axial position along an axis with a first orientationthat allows the first array, when phased, to project focused beams whichare respectively normal or nearly normal to a first target location onthe surface, a centerline of the first array and the first targetlocation lying in a plane; (b) while the array is in the first position,electrically pulsing respective groups of transducer elements of thefirst array using time delays in accordance with a first set of focallaws, which pulsing causes each pulsed group to emit a respectivefocused beam directed at the first target location at respectivesteering angles, the beams being emitted in sequence; (c) applying timedelays in accordance with the first set of focal laws to form respectivereturn signals from electrical signals output by the respective group oftransducer elements of the first array in response to emission of thefocused beams directed at the first target location; (d) selecting afirst return signal having a characteristic which indicates itcorresponds to an emitted beam that was normal or nearly normal to thepart surface at the first target location; (e) after steps (a) through(d) have been performed, positioning a second array of transducerelements at the axial position along the axis with a second orientationdifferent than the first orientation that allows the second array, whenphased, to project focused beams which are respectively normal or nearlynormal to a second target location on the surface, a centerline of thesecond array and the second target location lying in the plane; (f)while the second array is in the axial position, electrically pulsingrespective groups of transducer elements of the second array in sequenceusing time delays in accordance with a second set of focal laws, whichpulsing causes each pulsed group to emit a respective focused beamdirected at the second target location at respective steering angles;(g) applying time delays in accordance with the second set of focal lawsto form respective return signals from electrical signals output by therespective group of transducer elements of the second array in responseto emission of the focused beams directed at the second target location;(h) selecting a second return signal having a characteristic whichindicates it corresponds to an emitted beam that was normal or nearlynormal to the part surface at the second target location; and (i)displaying first and second pixels in a column, wherein the first pixelhas a value which is a function of at least a parameter value of thefirst return signal, and the second pixel has a value which is afunction of at least a parameter value of the second return signal.

In accordance with yet another aspect, a system for scanning a part isprovided comprising: an array of transducer elements; a shoe to hold thearray in a position with a steering plane; a pulser/receiver unitcapable of sending control signals to and receiving data signals fromthe array; and a computer system programmed with data acquisitionsoftware for controlling the pulser/receiver unit and data analysissoftware for selecting a respective best signal for each spatial elementof the part. The computer system is capable of operating in accordancewith the data acquisition software to control the pulser/receiver toperform the following operations: (a) electrically pulsing respectivegroups of transducer elements of the array in accordance with respectivefocal laws of a first set of focal laws to emit a plurality of focusedbeams in sequence, the focused beams being directed at different anglestoward a target location on a surface of the part; and (b) after eachrespective group of transducers is pulsed, receiving electrical signalsfrom the respective group in accordance with respective focal laws of asecond set of focal laws to form a respective return signal representinga respective echo returned to a respective group from the inspectedpart. The computer system is further capable of operating in accordancewith the data analysis software to perform the following operations: (c)processing the return signals to derive respective values of a parametercharacterizing the return signals; and (d) selecting one of therespective parameter values that satisfies a condition. The system mayfurther comprise a display monitor coupled to the computer system,wherein the computer system is further programmed with software forcontrolling the display monitor to display a pixel having a value whichis a function of at least the selected parameter value.

Other aspects are disclosed and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing two focused and steered beams transmitted atdifferent times from a linear ultrasonic transducer array and toward apart surface of unknown and variable shape.

FIG. 2 is a diagram showing an isometric view of a portion of anintegrally stiffened wing box with a radius of variable and unknownshape. The arrow indicates a direction of travel of the radius scannerdisclosed herein during inspection of the radius, which direction willbe referred to herein as the X-direction.

FIG. 3 is a flowchart showing steps of a method for ultrasonic dataacquisition in accordance with one embodiment.

FIG. 4 is a diagram showing an isometric view of a probe having threelinear ultrasonic transducer arrays arranged at respective angles inaccordance with one embodiment. The carriage and chassis are not shown.

FIG. 5 is a diagram showing an orthographic view of a portion of ageneralized integrally stiffened wing box of an airplane having top andbottom skins or panels connected by a plurality of spars.

FIG. 6 is a diagram showing a side view of a tractor-trailerconfiguration that includes an active trailer vehicle above and atractor vehicle below a bottom skin of an integrally stiffened wing box.(A passive trailer vehicle on the other side of the spar is notvisible.) The left-hand side of FIG. 6 shows an inspection scenariowherein the trailer vehicles are inverted, while the right-hand sideshows an inspection scenario wherein the tractor vehicle is inverted.

FIG. 7 is a diagram showing an end view of the tractor-trailerconfiguration depicted on the left-hand side of FIG. 6 (with respectiveinverted trailer vehicles disposed on both sides of a spar).

FIG. 8 is a diagram showing an end view of a probe in accordance with analternative embodiment. The probe is shown in its normal operatingposition. (The near-side magnet pods of the radius scanner are not shownfor clarity.)

FIG. 9 is a diagram showing an isometric view of the probe assemblydepicted in FIG. 8, but with electrical cabling omitted.

FIGS. 10 and 11 are diagrams showing back and bottom views of a radiusscanner in accordance with one implementation.

FIG. 12 is a diagram showing an isometric view of a probe/carriageassembly incorporated in the radius scanner depicted in FIGS. 10 and 11.

FIGS. 13 through 16 are diagrams which respectively show front, side,bottom and top views of the probe assembly depicted in FIGS. 8 and 9.

FIGS. 16A, 16B and 16C are diagrams showing respective sectional views,the sections being respectively taken along planes indicated by A-A, B-Band C-C in FIG. 16.

FIG. 17 is a block diagram showing a control system in accordance withone embodiment.

DETAILED DESCRIPTION

A process for non-destructive inspection of parts of variable andirregular shape will now be described. The process comprisestransmitting sequences of ultrasound beams at a multiplicity of targetlocations in each of a multiplicity of axially spaced planes anddetecting the best return signal for each target location to ensure thatthe sound enters the part at or nearly at 90 degrees or normal to theconfronting surface portion. It is important to keep the direction ofultrasound entry normal to the confronting surface. This process may,for example, be applied in inspection of soft-tooled composite parts,such as wing boxes comprising top and bottom external skins connected bya multiplicity of spars. The filleted join regions (i.e., radii) of suchparts, whether they are designed to be constant or to vary by partlocation, will “vary by manufacturing”. This fact creates a difficultand unique mechanical challenge to design and build an apparatus thatcan maintain sensor-to-part surface normality over a challenging andnot-known-in-advance variety of “radial” shapes. In accordance with oneimplementation, the ability to maintain normality over an unknown“radius” is provided using the data acquisition/analysis techniques andmechanical design described hereinafter.

One embodiment of a system having the ability to scan a part of variableand irregular shape will now be described with reference to a 64-elementlinear ultrasonic transducer array 44 shown in FIG. 1. For the purposeof illustration, the inspected part is made of composite material andcomprises a flange 46, a web 48 and a filleted join region 50, alsoreferred to herein as a “radius” (previously defined).

In accordance with one methodology, a sequence of ultrasonic beams istransmitted in a scan plane at different steering angles, all beamsbeing directed toward the same target location T. Specific orientationsof the sequentially transmitted ultrasound beams are achievedelectronically by phasing the elements in the array in accordance withstored focal laws. FIG. 1 shows two focused and steered beams B1 and B20respectively transmitted at the start and end of the aforementionedsequence of transmitted beams. The beams B1 and B20 are shown as beingdirected to a target location T on the surface of the radius 50.

In the embodiment shown in FIG. 1, the array 44 has 64 ultrasonictransducer elements respectively labeled E1 through E64. However, itshould be understood that the non-destructive inspection techniquesdisclosed herein do not require that the array have 64 elements. Thearray 44 could have more or fewer elements. Although FIG. 1 shows twobeams B1 and B20, it should be understood that beams B1 and B20 aretransmitted at different times and are only shown together in FIG. 1 forconvenience.

The intent of FIG. 1 is to depict an instance wherein array elements E20through E31 are sequentially activated in accordance with focal lawsdesigned to produce a focused beam B1 having a steering angle A1. Thevalue of steering angle A1 was selected such that beam B1 would bedirected at target location T. (The dashed lines indicate thecenterlines of beams B1 and B20.) Such a grouping of sequentiallyactivated elements will be referred to herein as an “aperture”. In theexample depicted in FIG. 1, the aperture consists of 12 elements. In thecase of beam B1, the aperture consists of elements E20 through E31.

FIG. 1 also depicts an instance wherein array elements E39 through E50are sequentially activated in accordance with focal laws designed toproduce a focused beam B20 having a steering angle A20. The value ofsteering angle A20 was also selected such that beam B20 would bedirected at target location T. In the case of beam B20, the apertureconsists of elements E39 through E50.

Although not shown in FIG. 1, for the purpose of this discussion it willbe assumed that the sequence of transmitted beams directed at target Tincludes 18 additional beams B2 through B19. In the case of beam B2, theaperture consists of elements E21 through E32; in the case of beam B3,the aperture consists of elements E22 through E33; and so forth. As iswell known to persons skilled in the art, for each transmitted beam thesame aperture will be employed to detect the echo response and convertthat echo response into a respective electrical return signal. Asexplained in more detail below, for each target location T, the returnsignals are processed to determine which return signal corresponds tothe beam that was closest to being normal to the part surface in thearea of target location T (or which return signals correspond to thebeams that were closest to being normal).

As is well understood in the art, one set of focal laws are applied whenthe elements of an aperture are transmitting while another set of focallaws are applied when the same elements transduce the echo response toform a return signal. The focal laws for transmitting and the focal lawsfor receiving are different yet related by the fact that they aredesigned to detect, for each transmit beam having a different steeringangle, a respective receive beam having the same steering angle. Forexample, the time delays applied to elements E20 through E31 fordetecting a receive beam having a steering angle A1 will be the same asthose used to transmit beam B1 having a steering angle A1. The sequencein which echo data is acquired from elements E20-E31 will be the reverseof the sequence in which those same elements were pulsed.

In accordance with the embodiment shown in FIG. 1, the position of array44 and the focal laws are selected for directing a sequence of beamsB1-B20 at target location T with different steering angles with the goalthat at least one beam will have a centerline perpendicular or nearlyperpendicular to the part surface in the area centered at targetlocation T. For such a ultrasound beam, refraction caused by off angleincidence to the part is minimal. In this instance, the ultrasound beamis the to be normal or nearly normal to the part.

FIG. 1 depicts a situation wherein neither beam B1 nor beam B20 isnormal to the part surface at target T. For the purpose of illustration,assume that all beams B1 through B20 have been transmitted and that abeam B8 (not shown in FIG. 1), produced by an aperture consisting ofelements E27 through E38, was normal or nearly normal to the partsurface at target T. In that event, the amplitude of the return signalgenerated by transducer elements E27-E38 in response to the echo derivedfrom impingement of beam B8 on the part should have the greatestamplitude of all of the return signals. A pixel value that is a functionof that greatest amplitude could then be displayed to indicate the stateof the inspected part at the target location T. (Alternatively, a pixelvalue that is a function of weightings applied to two or more returnsignal amplitudes meeting certain criteria could be displayed.) Thisprocess can be repeated for a multiplicity of targets arranged in rowsand columns to produce corresponding rows and columns of pixel values ona display screen (i.e., a computer monitor).

Depending on various factors, the system operator may determine how manybeams at different angles should impinge on each target location.Obviously, more beam angles could accommodate more distortion and radiusspread for a given application. Adversely, higher beam angle countrequires more system throughput in the phased array electronics.

FIG. 2 shows an isometric view of a portion of a composite part to beinspected. Again the inspected part comprises a flange 46, a web 48(forming an obtuse angle with the flange 46) and a radius 50 (having avariable surface). Using the technique described with reference to FIG.1, the radius 50 can be scanned in a series of parallel planes separatedby equal distances. This is accomplished by moving the ultrasonictransducer array(s) a predetermined incremental distance after eachplane has been scanned. The scanner travels along the length of the sparradius in an X-direction indicated by the arrow in FIG. 2. Oneembodiment of a suitable scanner will be described in detail later withreference to FIGS. 8-16.

The principle of scanning a target location with a multiplicity ofultrasound beams from different angles, detecting the best returnsignal, and then displaying a pixel value which is a function of thatbest return signal can be applied in many ways. The number of beamsdirected at each target location may vary within wide limits. Higherbeam counts require greater system throughput in the phased arrayelectronics.

FIG. 3 is a flowchart showing steps of a process for designing andimplementing a system for inspecting a portion of a part having asurface of unknown shape. The first stage in the process is to determinea shape of an inspection zone and a range of variation thereof (step70). Then a determination is made how to arrange one or more ultrasonictransducer arrays such that, when phased, these arrays can projectultrasound beams normal to targets to provide complete coverage of theinspection zone (step 72). This includes determining a position(including distance from the inspection zone and orientation relativethereto) of each ultrasonic transducer array such that, when phased,each array can project focused beams at a respective plurality of targetlocations in the inspection zone (i.e., each array scans a respectiveseparate section of the inspection zone). In step 74 the system designerdetermines respective sets of focal laws to interrogate the entire rangeof surfaces possible in the inspection zone. For example, if the surfaceof the inspected part again has a varying radius between 0.400 (minimum)and 0.600 (maximum) inch, for each array respective sets of targets canbe established along an arc length for a 0.500-inch radius midwaybetween the minimum and maximum radius dimensions using a CAD model. Foreach array, a respective set of focal laws can be determined for thetargets along the 0.500-inch radius.

Thereafter, the arrays are placed and oriented in accordance with thearray positions that were determined in step 72. During thenon-destructive inspection process, the elements of each array would bepulsed in accordance with its respective set of focal laws (step 76) sothat the array scans each target with respective focused beams atdifferent steering angles. Then after each respective group oftransducer elements has been pulsed to transmit a respective steeredbeam, the same transducer elements are used to detect returningultrasound waves from the inspected part and transduce the impingingultrasound waves into electrical signals, which electrical signals areselected using time delays to form a respective return signalrepresenting a respective received ultrasound beam having a centerlinethat intersects the target location of the inspected part. For each beamtransmitted by the array, the electrical return signals are processed toderive respective values of a parameter characterizing the returnsignals; then one of the respective parameter values that satisfies aspecified condition is selected. In one embodiment, the parameter can beamplitude and the specified condition is which return signal has thegreatest amplitude. In another embodiment, one or more other parametervalues that satisfy the same or other specified conditions can beselected. In a case where each array projects 20 beams at each target(as was the case shown in FIG. 1), then for each target the “best”return signal or the “best” two or more return signals can be selectedfrom the 20 return signals, wherein the term “best” is used in the senseof satisfying the specified conditions. Later the central computer canprocess the focal laws corresponding to the selected return signal(s) todetermine the vertical position of each target. For each interrogatedtarget location, the parameter value(s) of the best return signal(s)will be processed as a respective pixel value for display on a computermonitor or other display screen at a pixel location corresponding to thetarget location.

In accordance with one embodiment shown in FIG. 4, three linearultrasonic transducer arrays 44 a, 44 b and 44 c can be installed in aprobe body or shoe 52 and directed with different orientations towardrespective portions of a radius 50 having a variable and irregularshape. Each array is responsible for 30 degrees worth of inspectionalong a 90-degree arc length. In one embodiment, the array 44 a isoriented at a 75-degree angle, the array 44 b is oriented at a 45-degreeangle, and the array 44 c is oriented at a 15-degree angle. The shoe andarrays mounted therein form a probe 54 (also referred to herein as a“probe assembly”). As seen in FIG. 4, the probe 54 is located withrespect to the flange 46 and the web 48 of the inspected part. The probe54 is movable along the spar web (in the X-direction indicated in FIG.2). The probe 54 may be provided with bearings or wheels (not visible inFIG. 4) that contact the flange 46 and web 48, allowing the probe toroll in the X-direction.

Optionally, the probe 54 may be mounted on a chassis (not shown in FIG.4) that has two sets of magnets, one magnet set for coupling to opposingmagnets carried by a tractor vehicle (not shown in FIG. 4) disposedunder bottom skin and another magnet set for coupling to opposingmagnets carried by a second trailer vehicle (not shown in FIG. 4)disposed on the other side of web 48. The magnets hold the chassistightly against the flange and web. A system of this type will bedescribed in more detail later with reference to FIGS. 5-7.

The probe 54 is designed to keep the arrays 44 a-44 c at respectiveconstant distances from the web and flange, allowing the radiusdimension to vary underneath the arrays. Since each array is separatedby known distances from the web and flange, the aforementioned CAD modelis used to measure distances from the array elements to the radiustargets and establish beam angles through simple trigonometricfunctions. In accordance with the implementation described withreference to FIG. 1, apertures consisting of 12 elements are used tocreate the ultrasound beams at different steering angles. The steeringangle for each ultrasound beam can be determined by computing the angle(relative to the linear array) of a line extending from the center pointof each aperture to the target. During experimentation, arrays having apitch of 0.020 inch were used (“pitch” is the separation distancebetween the centers of adjacent array elements).

In accordance with one implementation, targets are established along anarc length of radius that is midway between the minimum and maximumradius dimensions of a surface of the part to be inspected. Forinstance, if the surface of the inspected part has a varying radiusbetween 0.400 and 0.600 inch, targets are established along the arclength for a 0.500-inch radius using a CAD model. The distance betweenthe targets at the 0.500-inch radius is selectable by the user but thereis a maximum distance established by the nondestructive inspection (NDI)requirements. If, for example, one wanted a target every 5 degrees, fora 90-degree application, there would be 18 targets equally spaced alongthe arc length.

Focal depth and aperture width (number of elements) are arrayconfiguration variables. A person skilled in the art may readily conductexperiments to optimize the configuration data. In one implementation,the array is configured and the pulser/receivers are programmed toproduce steered beams having a focal depth of roughly 2 inches. Thepulser/receiver may comprise a Tomoscan FOCUS LT phased arrayacquisition instrument commercially available from Olympus Corporation.Beams are created by the instrument after defining such variables aselement numbers, element spacing, velocity in the water, steering angle,etc. The beams are added into the firing sequence of the instrument andit fires them consecutively after a set distance of probe movement alongthe length of the composite part (e.g., in the X-direction seen in FIG.2). The set distance of probe movement serves as the scan resolution andthis distance is obtained from an encoder attached to the mobileplatform that carries the probe. Currently, because there are 20different angles for each target T along the radius arc length, it isadvantageous to use a respective pulser/receiver for each of the threearrays 44 a-44 c (see FIG. 4).

In accordance with one implementation, each scan plane is perpendicularto the X-axis and separated from adjacent scan planes by theaforementioned set distance. This spacing determines the horizontalresolution of the pixel image to be displayed. Preferably the resolutionis the same in the vertical direction, meaning that the targets will belocated along an arc length defined by the intersection of the scanplane and the radius. These targets will preferably be spaced apart bythe aforementioned set distance. In one implementation, 21 targets arelocated along a 90-degree arc length. The 75-degree array 44 a isoriented so that it can emit beams toward each of targets Nos. 1-7 insequence; the 45-degree array is oriented so that it can emit beamstoward each of targets Nos. 8-14 in sequence; and the 15-degree array isoriented so that it can emit beams toward each of targets Nos. 15-21 insequence. It should also be appreciated that arrays 44 a-44 c areaxially displaced relative to each other and can operate concurrently indifferent scan planes. For example, after array 44 a scans targets Nos.1-7 in the N-th scan plane, the probe will advance axially by the setdistance and then array 44 a will scan targets Nos. 1-7 in the (N+1)-thscan plane. If the distance separating the arrays 44 a-44 c is amultiple M times the set distance, then after M incremental advances bythe probe, the array 44 b will be in position to scan targets Nos. 8-14in the N-th scan plane. Similarly, after another M incremental advancesby the probe, the array 44 c will be in position to scan targets Nos.15-21 in the N-th scan plane.

Table 1 below is an example of a group of beams that can be transmittedfrom the 45-degree array 44 b. A CAD model was used to create thistable. Row 8 corresponds to the 8-th target on the radius. The firstcolumn labeled “Fire Gp No.” in Table 1 is the number of the group ofelements (also referred to herein as the “aperture”) which are fired toemit a focused steered beam, which group number corresponds to thenumber of the lowest-numbered element in that group. In the exampleshown in Table 1. “Fire Gp No. 20” means to fire a group of 12 elements(i.e., aperture width equals 12) starting with element 20 to form abeam. In this example, Fire Gp No. 20 includes elements E20-E31 of a64-element linear array. As seen in the second column (labeled “AryAng”) of Table 1, the steering angle of Fire Group No. 20 is −8.8degrees. The parameter “Part Angle” in the fourth column (labeled “PrtAng”) shows the degree to which the beam having a steered angle of −8.8degrees is off normal to the inspected part (i.e., the surface areasurrounding the 8-th target). The fifth column (labeled “Refr Ang”)indicates the angle of refraction of the transmitted beam. Roughly inthe middle of this group of beams (i.e., Fire Group No. 30), the partangle and refraction angle are near zero. One should expect thestrongest response to come from this beam, provided that the part'sradius aligns with the CAD model used to create Table 1.

Table 1 also includes a third column (labeled “Δdb Gain”) which showsrespective values for a delta decibel gain. Experiments have shown thatultrasonic waves propagating through water (or other acoustic couplant)attenuate with beam angle. The attenuation versus steering beam anglewas measured while holding the distance constant. The attenuation is, atleast in part, a function of the inefficiency of energy at the higherangles. The propagation distance is assumed to be equal to the length ofthe beam centerline, which extends from the center of the aperture tothe target location. To compensate for the loss due to attenuation,respective values of an instrument gain are introduced for the steeringangles. Higher steering angles require more instrument gain.

Table 1 presents data for a group of 20 beams which can be fired at one(i.e., the 8-th) target from different directions. In accordance withone implementation, the 45-degree array transmits respective groups ofbeams directed at 7 (i.e., the 8-th through 14-th) targets, resulting in140 beams. In other implementations, the targets can be closer together,resulting in more than 7 targets located along a 30-degree arc length.Also, in accordance with other implementations, the number of steeredbeams directed toward each target location can be more or less than 20.

TABLE 1 Row 8 Fire Gp No. Ary Ang Δdb Gain Prt Ang Refr Ang 20 −8.8 1.1112.5 27.9 21 −10.2 1.56 11.1 24.8 22 −11.5 2.03 9.8 21.7 23 −12.8 2.508.5 18.8 24 −14.1 3.00 7.2 15.8 25 −15.3 3.68 6.0 13.0 26 −16.6 4.41 4.710.2 27 −17.9 5.13 3.4 7.5 28 −19.1 5.77 2.2 4.8 29 −20.3 6.40 1.0 2.230 −21.5 7.04 −0.2 −0.4 31 −22.7 7.73 −1.4 −2.9 32 −23.8 8.40 −2.5 −5.533 −24.9 9.01 −3.6 −7.9 34 −26.1 9.67 −4.8 −10.4 35 −27.1 10.38 −5.8−12.8 36 −28.2 11.21 −6.9 −15.2 37 −29.3 12.28 −8.0 −17.5 38 −30.3 13.32−9.0 −19.8 39 −31.3 14.50 −10.0 −22.1

In accordance with one application, the method described above can beused in the non-destructive inspection of an integrally stiffened wingbox of an aircraft e.g., a horizontal stabilizer made of compositematerial. A portion of a generalized integrally stiffened wing box 2 isdepicted in FIG. 5. The depicted integrally stiffened wing box comprisesa top skin 4 and a bottom skin 6 connected by a plurality of internalvertical support elements, hereinafter referred to as “spars”. Each sparcomprises a web 8 and respective pairs of filleted join regions 10 (alsocalled “spar radii” herein), which connect the spar web 8 to the top andbottom skins. As used herein, the terms “top skin” and “bottom skin”refer to the relative positions of two skins of a wing box duringinspection, not when the wing box is installed on an airplane (i.e., awing box may be inverted for inspection).

In accordance with one embodiment, a probe (comprising a shoe and one ormore linear ultrasonic transducer arrays) is transported down the lengthof a tunnel through the interior of a hollow composite structure. Forthis type of inspection, the probe is carried by a trailer vehicle (notshown in FIG. 5) placed inside the hollow structure 2. This trailervehicle can be characterized as being “active” in the sense thatequipment it carries is actively performing a scanning function. Eacharray needs to be acoustically coupled to each surface being inspected.This is accomplished by providing a column of water that flows betweenthe array and the inspected part. An automated tractor vehicle (also notshown in FIG. 5) moves the active trailer vehicle along the spar web 8.

In FIG. 5, portions of the interior surfaces of the part which need tobe inspected can be seen. Each spar may need to have all four filletedjoin regions 10 and each web 8 inspected. This is a challenginginspection as each cavity is essentially a long rectangular tunnel thatmay increase or decrease in cross section as one moves from one end tothe other. The top and bottom skins 4 and 6 can be inspected from theexterior using conventional NDI techniques which are not part of thisdisclosure

In accordance with one embodiment for inspecting structures of the typeshown in FIG. 5, an external motorized and computer-controlled tractoris magnetically coupled to an internal active trailer that holds andpositions one or more ultrasonic transducer arrays on the interior ofthe part. Also, there is an internal passive trailer on the oppositeside of the spar that is magnetically coupled through the spar to theactive trailer and also magnetically coupled through the skin to thetractor. This three-part system gives a very stable system forpositioning and moving the ultrasonic transducers. One embodiment ofsuch a three-part system will now be described with reference to FIGS. 6and 7.

FIG. 6 shows side views of a tractor-trailer configuration in accordancewith one embodiment in two different inspection situations (motoractuators are not shown). The automated NDI inspection system comprisesa traction-motor powered tractor vehicle 12, which rides on the externalsurface of top skin 4 or bottom skin 6 of integrally stiffened wing box2, and a pair of trailer vehicles (only trailer vehicle 14 is visible inFIG. 6, the other being hidden behind a spar web 8), which ride along aninternal surface of the top or bottom skin. The left-hand side of FIG. 6shows an inspection scenario wherein the tractor vehicle 12 is outsidethe integrally stiffened wing box in a non-inverted position while thetrailer vehicles are inside the integrally stiffened wing box ininverted positions; the right-hand side of FIG. 6 shows an inspectionscenario wherein the tractor vehicle 12 is outside the integrallystiffened wing box in an inverted position while the trailer vehiclesare inside the integrally stiffened wing box in non-inverted positions.FIG. 7 shows an end view of the tractor-trailer configuration depictedon the left-hand side of FIG. 6, with inverted trailer vehicles 14 and16 disposed on opposite sides of the spar web.

In the inspection scenario depicted in FIG. 7 (and the left-hand side ofFIG. 6), idler wheels 18 of tractor vehicle 12 contact and roll on theexternal surface of top skin 4 while vertical idler wheels 20 ofinverted trailer vehicles 14 and 16 (only one such idler wheel isvisible in FIG. 7 for each trailer vehicle) contact and roll on theinternal surface of top skin 4, and the horizontal idler wheels 22 rollon the spar web surface. The right-hand side of FIG. 6 shows analternative situation wherein idler wheels 18 of the inverted tractorvehicle 12 contact and roll on the external surface of bottom skin 6while vertical idler wheels 20 of trailer vehicle 14 (and also idlerwheels of trailer vehicle 16 not visible in FIG. 6) contact and roll onthe internal surface of bottom skin 6, and the horizontal idler wheels22 roll on the spar web surface.

In accordance with the embodiment partly depicted in FIGS. 6 and 7, thetractor vehicle 12 comprises a frame 24. Four idler wheels 18 (only twoof which are visible in each of FIGS. 6 and 7) are rotatably mounted toframe 24 in a conventional manner. (Alternative embodiments may includemore idler wheels.) The idler wheels 18 are made of plastic and havesmooth contact surfaces. Tractor vehicle motion is enabled by driving adrive wheel 26 (also rotatably mounted to frame 24) to rotate. Drivewheel 26 is coupled to a motor 30 via a transmission (not shown). Thedrive wheel 26 is positioned on the frame 24 so that it is in frictionalcontact with skin 4 or 6 when idler wheels 18 are in contact with thesame skin. The drive wheel is made of synthetic rubber material. Thesurface of the drive wheel may have a tread pattern. In addition, thetractor vehicle 12 carries multiple permanent magnets 28. Each permanentmagnet 28 has North and South poles, respectively indicated by letters“N” and “S” in the drawings.

Still referring to FIGS. 6 and 7, each trailer vehicle 14, 16 iscomprised of a frame 34. For each trailer vehicle, two vertical idlerwheels 20 (only one of which is visible in FIG. 7) and four horizontalidler wheels 22 (only two of which are visible in FIG. 7) are rotatablymounted to frame 34 in a conventional manner. (Alternative embodimentsmay include more idler wheels.) Each trailer vehicle 14, 16 carriesmultiple vertically mounted permanent magnets 36, the North poles ofwhich are magnetically coupled to the South poles of confrontingpermanent magnets 28 carried by the tractor vehicle 12. In the designdescribed by FIGS. 6 and 7, each trailer has two vertically mountedpermanent magnets 36, but other designs may use differentconfigurations. The positions and pole orientations of the magnets mayhave other configurations as long as the N-S pairing and relativealignment of the magnets between the tractor and trailer are preserved.

As seen in FIG. 7, in addition to being magnetically coupled to thetractor vehicle 12, the trailer vehicles 14 and 16 are magneticallycoupled to each other using additional sets of permanent magnets 38 and42. As seen in FIG. 6, trailer vehicle 14 carries four horizontallymounted permanent magnets 38. Trailer vehicle 16 also carries fourhorizontally mounted permanent magnets 42 (only two of which are visiblein FIG. 7), the poles of which are respectively magnetically coupled toopposing poles of the permanent magnets 38 on trailer vehicle 14. Thismagnetic coupling produces an attraction force that holds idler wheels22 of trailer vehicles 14 and 16 in contact with opposing surfaces of anintervening spar.

As seen in FIG. 6, trailer vehicle 14 further carries a payload 40. Forthe NDI scenario depicted in FIGS. 6 and 7, payload 40 is a probeassembly comprising a shoe with three linear ultrasonic transducerarrays disposed at three different angles. As previously noted, thearrays must be acoustically coupled to the surface being inspected. Forexample, the inspected region is covered with a constant stream of waterto acoustically couple the ultrasonic sensor to a filleted join region10. Magnetically coupled systems are well suited for operation withwater in the environment.

As the tractor vehicle is driven to travel along a desired path on theouter surface of the top or bottom skin, it pulls the inner trailervehicles along. The magnetic coupling system described above keeps theinverted vehicle(s) in contact with the surface it rides on. For wingbox applications, two magnetically coupled trailer vehicles can be used,one on each side of the spar, as shown in FIG. 7. This allows the systemto take advantage of the internal structure of the scanned object as aguide to allow the system to track properly along the surface.

The system partly depicted in FIGS. 6 and 7 further comprises means (notshown) for automatically adapting to the variable thickness of theintervening skin or panel (i.e., top skin 4 or bottom skin 6) by raisingor lowering the magnets (which magnet motion is indicated bydouble-headed arrows in FIG. 6) on the tractor vehicle as it moves alongthe structure being inspected. Further details concerning thetrailer-tractor configuration depicted in FIGS. 6 and 7 (and alternativeembodiments) are disclosed in U.S. patent application Ser. No.13/313,267, the disclosure of which is incorporated by reference hereinin its entirety.

An apparatus for inspecting filleted join regions 10 (hereinafter“radii”) of an elongated and tapered hollow structure will now bedescribed. The active trailer vehicle for scanning a spar radius will bereferred to herein as a “radius scanner”. In the embodiment shown inFIG. 7, the trailer vehicle 14 is designed to work with the tractor onthe top or bottom of the integrally stiffened wing box (or othercomposite structure having cavities between webs). The radius scanner 14carries a probe that operates as previously described under the controlof a computer that host data acquisition/analysis software. The radiusscanner may also have a video camera (not shown) that captures a liveview of the probe.

The X-axis motion (the X axis being parallel to the spar radius beinginspected if the spar radius is linear) is provided by the tractorvehicle of the system, which uses data from a rotational encoderattached to an idler wheel on the trailer vehicle. The trailer componentis pulled by the tractor and carries the probe assembly. The X-motiondrive motor can be a programmable stepper motor that can communicatewith the computer through a serial communications interface. Theoperator or automated path planning system specifies the desiredincremental movements, direction, and an optional final goal position ofthe tractor-trailer system through a motion control softwareapplication. The X-axis positioning is controlled using proportionalfeedback of the encoder count data.

One implementation of a radius scanner equipped with a scanning systemthat employs linear phased arrays in the manner described above will nowbe described with reference to FIGS. 8-16. This implementation differsfrom the embodiment depicted in FIG. 4 in the respect that the threearrays are not held in fixed positions by a single probe body. Insteadthe 15-degree and 45-degree arrays are fixed in respective cavities of aweb rider body, while the 75-degree array is carried by a flange riderthat can pivot relative to the web rider body. This arrangement will bedescribed in detail below.

FIG. 8 shows an end view of a radius scanner with its probe 54 in itsnormal operating position relative to portions of a wing box, includinga bottom skin 6, a spar web 8, and a radius 10. (The near-side magnetpods of the radius scanner are not shown in FIG. 8 for clarity). Thethicker portions of bottom skin 6 adjacent spar web 8 are referred toherein as flanges 46. The radius scanner comprises a carriage frame 80that supports the probe assembly 54 by means of links (including asocket link 112 b disposed in a slot 114 b seen in FIG. 8, but describedin detail later with reference to FIG. 12).

The probe assembly 54 comprises a web rider body 55 that supports the15- and 45-degree arrays in fixed positions and further supports apivotable flange rider 57 that holds the 75-degree array. The flangerider 57 is pivoted so that the 75-degree array will always be parallelto the flange surface as the manufactured angle between web and flangevaries along the length of the part. The web rider body 55 has a set offour web rider wheels 58 (only two of which are visible in the FIG. 8)which contact the web 8. The carriage frame 80 has a pair of wheels 81(only one of which is visible in FIG. 8) which contact the flange 46.FIG. 8 also shows a single flange rider wheel 59, which is shown in moredetail in FIGS. 13 and 16A (described later). Wheel 59 is rotatablymounted on the flange rider 57. As depicted in FIG. 8, the flange riderwheel 59 does not always contact the part, depending on which portion ofthe part is being inspected. The flange rider 57 has a pair of rubbingridges 60 which are provided for places where the flange 46 does notextend out to the flange rider wheel 59.

FIG. 9 shows an isometric view of a probe assembly in accordance withone embodiment in which the ultrasonic arrays are held by a web riderbody 55 and a flange rider 57 pivotably mounted in a cavity in the webrider body 55. This probe assembly is incorporated in the probe/carriageassembly depicted in FIG. 12. (However, other probe assemblies can beused with the probe/carriage assembly depicted in FIG. 12.) The45-degree array 44 b and 15-degree array 44 c are fixed insiderespective cavities formed in the web rider body 55. The 75-degree array44 a is carried by the pivotable flange rider 57.

FIG. 8 also shows the signal cabling for the ultrasonic transducerarrays, including cable 61 which is connected to the 15-degree array,cable 63 which is connected to the 45-degree array, and cable 65 whichis connected to the 75-degree array. Cable 122 is connected to theX-position encoder (described with reference to FIG. 11 below). Theelectrical cabling has been omitted from FIG. 9 to allow a clear view ofthe ultrasonic transducer arrays 44 a-44 c.

Ultrasonic inspection at the frequency used by the system disclosedherein requires the presence of an acoustic couplant between eachultrasonic transducer array and the inspected part. The scanning systemshown in FIG. 8 uses water as the acoustic couplant. The probe 54 hasthree water cavities (not shown in FIG. 8, but see items 110 a-c inFIGS. 16A-C respectively)) which are supplied with water via a watersupply tube 64 that is connected to an inlet of a water manifold (notshown in FIG. 8). FIG. 9 shows the inlet 66 of water manifold 68. Wateris supplied from the manifold 68 to the water cavity for array 44 a bymeans of a tube 62. Water is supplied to the water cavities for arrays44 b and 44 c by means of the water manifold 68. More details will beprovided later when FIGS. 16A-16C are described.

In accordance with one implementation, the carriage frame 80 is part ofa chassis that is magnetically coupled to a tractor vehicle and to apassive trailer vehicle, as previously described with reference to FIGS.6 and 7. The chassis and probe assembly form an active trailer vehiclethat will hereinafter be referred to as a “radius scanner”. The chassiswill be described in detail with reference to FIGS. 10 and 11.

FIGS. 10 and 11 show back and bottom views of a radius scanner inaccordance with one implementation. As best seen in FIGS. 10 and 11,this radius scanner comprises a rigid carriage frame 80 having two sidemembers 80 a and 80 b, a back 80 c which connects the rear end of theside members 80 a-b, and ribs 80 d and 80 e which connect to back 80 cand to the respective side members 80 a-b.

The radius scanner shown in FIGS. 10 and 11 will be magnetically coupledto a tractor vehicle on the other side of a flange by means of twothrough-flange magnet trolleys 90 a, 90 b and magnetically coupled to apassive trailer vehicle on the other side of a web by means of twothrough-web magnet trolleys 92 a, 92 b. Each magnet trolley carries apair of magnets 94 for magnetic coupling to magnets of opposite polaritycarried by the tractor vehicle and other trailer vehicle, as previouslydescribed. Each through-web magnet trolley has four wheels 98, whichcontact a web surface. Each through-flange magnet trolley has two wheels100, which contact a flange surface. As best seen in FIG. 11, eachthrough-flange magnet trolley 90 a, 90 b is adjustably mounted to acorresponding through-web magnet trolley 92 a, 92 b. The latter, inturn, are respectively rigidly connected to respective side members 80a, 80 b of the carriage frame 80. A video camera 96 (with sceneillumination lamps) is mounted on through-web magnet trolley 92 b (seeFIG. 10). The video camera 96 monitors operations, sending video imagesback to the central computer via a cable 97.

Referring to FIG. 11, the X-position of the probe 54 is measured by anX-direction encoder 102, which encodes rotation of an encoder wheel 104mounted to the carriage frame 80. The encoder wheel 104 rides on the websurface as the radius scanner travels along a radius. The encoder wheel104 is shown in FIG. 10 in its extended position, which occurs when theradius scanner is separated from the web surface (i.e., no longer incontact). The encoder 102 sends an encoder pulse to the operationscontrol center (via encoder cable 122) after each incremental movementof the scanner in the X-direction, which encoder pulses are used by acontrol computer and by ultrasonic pulser/receiver devices to determinethe X-coordinate of each scan plane in a well-known manner.

The water supply tube 64, the signal cabling (items 61, 63 and 65 inFIG. 8) for the ultrasonic transducer arrays, the camera cable 97 andthe encoder cable 122 all pass through a supply umbilical 120 (see FIG.10) which connects the radius scanner to the operations control center.The water supply tube 64 is connected in this way to a water supply (notshown in the drawings) The signal cabling for the ultrasonic arrays isconnected the pulser/receiver devices (not shown in FIGS. 10 and 11).Video from the camera is received by a display monitor (item 134 in FIG.17) via a camera switch (not shown in the drawings). The encoder pulsesare ultimately received by the ultrasonic pulser/receiver devices andthe control computer (items 82 and 84 in FIG. 17), as previouslydescribed.

FIG. 12 shows an isometric view of a probe/carriage assemblyincorporated in the radius scanner depicted in FIGS. 10 and 11. Theprobe/carriage assembly comprises a web rider body 55 supported by aflex carriage. The flex carriage comprises carriage frame 80 and a setof linkages which bias the web rider body 55 against the radius atroughly an angle that bisects the angle between the web and the flangesurfaces. This allows the probe assembly to passively adjust itsposition while held in contact with internal surfaces of the spar weband adjacent skin. In this implementation, the flex carriage supportsthe web rider body 55 in a manner that allows the latter to traveltoward/away from a radius by a total travel distance of less than ¼ inchduring normal operation. A person skilled in the art will recognize thata flex carriage could be designed to achieve any desired total traveldistance. Because the carriage frame 80 can move sideways on the webinto the flange, the web rider body 55 also has a pair of web riderflange-stop wheels 56 which stop the web rider body from contacting theflange. A pair of compression springs 126 push the pivotable flangerider 57 into the flange (not shown).

Still referring to FIG. 12, the flex carriage is coupled to the probeassembly 54 by means of a pair of ball-and-socket joints 106 a and 106b. Each ball-and-socket joint comprises a respective socket link 108a/108 b (hereinafter “first and second socket links”), which are partsof the flex carriage, and a respective ball link (hereinafter “first andsecond ball links”), which are parts of the probe assembly. The flexcarriage further comprises a pair of arms 110 a and 110 b. The firstsocket link 108 a is fastened to one end of arm 110 a; the second socketlink 108 b is fastened to one end of arm 110 b. In addition, each sidemember 80 a,b has a respective slot 114 a,b in which third and fourthsocket links are respectively coupled to third and fourth ball links(not visible in FIG. 12) to form third and fourth ball-and-socketjoints. The only components of the third and fourth ball-and-socketjoints visible in FIG. 12 are the third and fourth socket links 112 a,b.The slots 114 a,b are both disposed at an angle roughly equal to 45degrees and have a slot width which limits the angular travel of socketlinks 112 a,b from a pressure plane. The first and second socket links108 a and 108 b are oriented to limit angular travel off normal to thepressure plane. Slight motion in the directions indicated by thedouble-headed arrow A in FIG. 12 is taken up by the tolerances in theball-and-socket joints.

The flex carriage shown in FIG. 12 further comprises a pair of flexspring arm anchors 116 a and 116 b which can be attached to arms 110 aand 110 b respectively, the positions of the former relative to thelatter being adjustable. The probe 54 further comprises a pair of flexspring probe anchors 118 a and 118 b. The opposing arm and probe anchorsare coupled by means of respective flex springs 120 a and 120 b. One endof flex spring 120 a is hooked onto arm anchor 116 a and the other endis hooked onto probe anchor 118 a; one end of flex spring 120 b ishooked onto arm anchor 116 b and the other end is hooked onto probeanchor 118 b. These springs provide a biasing force. The net force isinto the web/flange joint, leaving enough freedom of motion to allow theprobe body to follow the uneven surface on its own contact wheels.

The implementation depicted in FIGS. 10-12 is only one way of pressingthe probe body into the radius. The same functionality could be achievedusing apparatus of different designs.

In accordance with an alternative embodiment, the probe assembly couldbe driven (e.g., by a stepper motor) to pivot about an axis that isparallel to the X-direction. In that case, an array could transmit onegroup of beams toward an N-th target while the probe assembly isstationary; then the probe assembly would be rotated about its pivotaxis by a specified number of degrees (e.g., 5 degrees); then the arraycould transmit another group of beams toward an (N+1)-th target whilethe probe assembly is again stationary; and so forth.

FIGS. 13 through 16 show front, side, bottom and top views of the probeassembly depicted in FIG. 9. FIG. 13 shows a pair of flange rider springposts 140 a,b. Respective ends of compression springs 126 shown in FIG.12 are hooked onto flange rider spring posts 140 a,b, enabling thesesprings to bias the flange rider to pivot in a direction toward theflange. FIG. 14 shows the flange rider pivot axis 128. The probeassembly comprises a pair of strongbacks 122 and 124 which mechanicallystabilize the far end of the flange rider pivot axis. FIG. 15 shows theprobe assembly 54 seen in FIG. 11, but on a magnified scale.

FIGS. 16A, 16B and 16C are diagrams showing respective sectional views,the sections being respectively taken along planes indicated by A-A, B-Band C-C in FIG. 16. Section A-A passes through the 75-degree array 44 c;section B-B passes through the 45-degree array 44 b; and section C-Cpasses through the 15-degree array 44 a.

The section plane for FIG. 16A also passes through the flange riderwheel 59, which comprises the outer race of a roller bearing whose innerrace is held in a fixed position by a screw 132. The flange rider wheel59 rides on the flange (where the flange is wide enough to engage it).In some places the part flange is a bit narrower, and the flange riderslides along on plastic rubbing ridges 60. The function of both of theseis to hold the flange rider at a constant distance from the planarsurface of the flange.

As seen in FIG. 16A, the flange rider 57 comprises a passageway 30 whichis in fluid communication with tube 62. Water supplied via tube 62 flowsthrough passageway 130 and another internal passageway (not shown), andthen enters the water cavity 110 a via a water inlet 112 a. Referring toFIGS. 16B and 16C, water from the water manifold 68 flows onto watercavities 110 b and 110 c via respective water inlets 112 b and 112 c.The supply of water should be sufficient to continuously fill all of thewater cavities 110 a-c during scanning operations.

FIG. 17 is a block diagram showing a control system in accordance withone embodiment. The control system comprises a ground-based computer 84programmed with motion control application software 86 and NDI scanapplication software 88. The control computer 84 is connected to thedrive tractor platform (previously referred to as a “tractor vehicle”)and to the radius scanner by flexible electrical cables that connect toan electronics box (not shown). The electronics box contains the systempower supplies and integrates all the scanner control connections andprovides an interface between the computer, drive tractor, and radiusscanner.

The computer 84 may comprise a general-purpose computer programmed withmotion control application software 86 comprising respective softwaremodules for controlling drive motor 138 and magnet vertical positioningmotors 140 onboard the drive tractor platform. The magnet motors 140displace the tractor coupling magnets 28 as disclosed in U.S. patentapplication Ser. No. 13/313,267.

The motion control application software 86 also controls a motor of acable management system 136. The cable management system 136 consists oftwo sets of motorized wheels that respectively grip the cablesconnecting the operations control center to the tractor and radiusscanner. The motor of the cable management system is under computercontrol, which synchronizes the cables with the movement of the radiusscanner and the tractor, extending or retracting the cables asappropriate.

In accordance with one embodiment, the encoded data from encoder 102 isreceived by three ultrasonic pulser/receiver devices 82, which in turnsend those encoder pulses to the NDI scan software 88. The NDI scanningsoftware application 88 uses these pulses to position the scan data inthe proper location on a display monitor 134. An offset for each arrayis used for final display. The offset corresponds to the physicaldistance between the arrays in the array housing. The pixel columnshaving values derived from data acquired in the same scan plane by eacharray are aligned as one in the final display.

The NDI scan application 88 includes ultrasonic data acquisition anddisplay software that controls the ultrasonic pulser/receiver devices82. The ultrasonic pulser/receiver devices 82 in turn send pulses to andreceive return signals from the ultrasonic transducer arrays 44 a-c. TheNDI scan application software 88 controls all details of the scan dataand the display of data. The pulser/receiver devices 82 correlate theacquired ultrasonic data with the X-position information.

One embodiment of the control system depicted in FIG. 17 has the abilityto provide meaningful distance information in a final C-scan. The C-scanpresentation provides a plan-type view of the location and size of partfeatures. The plane of the image is parallel to the scan pattern of thetransducer arrays. In a C-scan, there is distance information shown inthe display. The distance information is found along the horizontal andvertical axes (or rulers) of the display. Individual pixels make up theC-scan. The width of the pixel directly corresponds to the resolution ofthe dimensional encoder 102 running along the horizontal axis of thepart. However, the distance in the vertical direction must correlate tothe distance between the beams directed at different targets in a scanplane. Set targets are provided along each radius arc length. Sincegroups of beams are hitting each target, the distance between the groupsof beams corresponds to the physical distance between the targets.Eventually, operators will have to make area measurements of flaws thatmight show up in the C-scan. This would be hard to do if all the beamswere displayed in the C-scan because multiple beams would be hitting thesame target and there would be redundancy in the area measurements.However, if a selected focal law is used from each group of beams, thedistance between the theoretical targets directly correlates to theheight of the C-scan pixels. Optionally, this beam selection can be doneduring post-processing after the part has been scanned. The NDI scanapplication includes data analysis software which is used to determinethe best return signals according to the method previously described.The best return signals may be derived from front surface echoes, fromback surface echoes, by calculating a weighted function of two or morefront surface echoes, by recording all echoes within an internal gate,or any other suitable means.

While various embodiments have been described, it will be understood bythose skilled in the art that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the teachings herein. In addition, many modificationsmay be made to adapt a particular situation to the teachings hereinwithout departing from the scope thereof. Therefore it is intended thatscope of the claims set forth hereinafter not be limited to thedisclosed embodiments.

As used in the claims, the term “computer system” should be construedbroadly to encompass a system having at least one computer or processor,and which may have two or more interconnected computers or processors.

The method claims set forth hereinafter should not be construed torequire that the steps recited therein be performed in alphabeticalorder or in the order in which they are recited. Nor should they beconstrued to exclude any portions of two or more steps being performedconcurrently.

The inventiom claimed is:
 1. A method comprising: (a) determining an arcthat approximates a curved concave profile of a radiused surface of apart; (b) determining first focal laws for interrogating the radiusedsurface such that an ultrasonic transducer array, when pulsed withproper phasing in accordance with the first focal laws, will projectrespective sequences of focused and steered beams that are directed atrespective target locations spaced along an arc having the same radiusas the arc determined in step (a); (c) placing an ultrasonic transducerarray at a first position whereat a first scan plane of the ultrasonictransducer array intersects the radiused surface; (d) while theultrasonic transducer array is stationary at the first position, pulsingthe ultrasonic transducer array in accordance with first focal lawsdetermined in step (b) to interrogate a first target location in thefirst scan plane by transmitting a first sequence of focused and steeredultrasonic beams that are directed toward the first target location atdifferent steering angles; (e) forming a first sequence of respectivereturn signals representing respective receive beams returned to theultrasonic transducer array from the first target location followingtransmission of each focused and steered ultrasonic beam of the firstsequence of focused and steered ultrasonic beams; (f) processing thefirst sequence of return signals to generate a first multiplicity ofparameter values, each value representing a magnitude of acharacteristic of a respective return signal of the first sequence ofreturn signals; and (g) selecting a first parameter value from the firstmultiplicity of parameter values that satisfies a condition configuredto identify a best return signal of the first sequence of returnsignals.
 2. The method as recited in claim 1, wherein the parametervalues are amplitudes and the condition is having a greatest amplitude.3. The method as recited in claim 1, further comprising displaying afirst pixel having a first pixel value which is a function of at leastthe first parameter value.
 4. The method as recited in claim 3, furthercomprising selecting a second parameter value of the first multiplicityof parameter values that satisfies the condition, wherein the firstpixel value is a function of the first and second parameter values. 5.The method as recited in claim 3, further comprising: while theultrasonic transducer array is stationary at the first position, pulsingthe ultrasonic transducer array in accordance with second focal lawsdetermined in step (b) to interrogate a second target location in thefirst scan plane by transmitting a second sequence of focused andsteered ultrasonic beams that are directed toward the second targetlocation at different steering angles; forming a second sequence ofreturn signals representing respective receive beams returned to theultrasonic transducer array from the second target location followingtransmission of each focused and steered ultrasonic beam of the secondsequence of focused and steered ultrasonic beams; processing the secondsequence of return signals to generate a second multiplicity ofparameter values, each value representing a magnitude of acharacteristic of a respective return signal of the second sequence ofreturn signals; selecting a second parameter value from the secondmultiplicity of parameter values that satisfies a condition configuredto identify a best return signal of the second sequence of returnsignals; and displaying a second pixel having a second pixel value whichis a function of at least the second parameter value, wherein the firstand second pixels are displayed in one column on a display screen. 6.The method as recited in claim 1, further comprising: moving theultrasonic transducer array from the first position to a second positionwhereat a second scan plane of the ultrasonic transducer arrayintersects the radiused surface; while the ultrasonic transducer arrayis stationary at the second position, pulsing the ultrasonic transducerarray in accordance with the first focal laws to interrogate a secondtarget location in the second scan plane by transmitting a secondsequence of focused and steered ultrasonic beams that are directedtoward the second target location at different steering angles; forminga second sequence of return signals representing respective receivebeams returned to the ultrasonic transducer array from the second targetlocation following transmission of each focused and steered ultrasonicbeam of the second sequence of focused and steered ultrasonic beams;processing the second sequence of return signals to generate a secondmultiplicity of parameter values, each value representing a magnitude ofa characteristic of a respective return signal of the second sequence ofreturn signals; selecting a second parameter value from the secondmultiplicity of parameter values that satisfies a condition configuredto identify a best return signal of the second sequence of returnsignals; and displaying a second pixel having a second pixel value whichis a function of at least the second parameter value, wherein the firstand second pixels are displayed in one row on a display screen.
 7. Amethod comprising: (a) determining a radius of an inspection arcsuitable for inspecting a radiused surface of a part having a curvedconcave profile; (b) determining a position of an ultrasonic transducerarray relative to the radiused surface such that, when properly phased,the ultrasonic transducer array is capable of projecting focused beamsat a plurality of target locations spaced along the inspection arc; (c)determining focal laws for interrogating each of the plurality of targetlocations spaced along the inspection arc using a respective sequence offocused beams having different steering angles for each target location;(d) positioning the ultrasonic transducer array in the positiondetermined in step (b); (e) pulsing the ultrasonic transducer array inaccordance with the focal laws determined in step (c); (f) formingrespective return signals representing respective receive beams returnedto the ultrasonic transducer array from the part following pulsing instep (e); and (g) selecting a respective parameter value of a respectivebest return signal for each interrogated target location.
 8. The methodas recited in claim 7, further comprising: displaying respective pixelshaving respective pixel values, each pixel value being a function of atleast a respective selected parameter value.
 9. The method as recited inclaim 8, wherein the target locations lie in a scan plane and therespective pixels are displayed in a column on a display screen.
 10. Themethod as recited in claim 8, wherein step (c) comprises determiningfocal laws for interrogating target locations which are spaced at equaldistances along an inspection arc having a radius approximating a radiusof the radiused surface.
 11. The method as recited in claim 7, furthercomprising supplying fluid acoustic couplant into a space between theultrasonic transducer array and the part, wherein step (f) comprisesapplying respective gains to the respective return signals, the gainsbeing selected to compensate for different amounts of attenuation causedby fluid acoustic couplant in the space between the ultrasonictransducer array and the part, the respective gains being a function ofdistance of travel of each echo through the fluid acoustic couplant. 12.A method for inspecting a radiused surface having a curved concaveprofile, the method comprising: positioning an array of transducerelements at a first position along an axis with an orientation thatallows the array, when properly phased, to project focused beams whichare respectively normal or nearly normal to first and second targetlocations on the radiused surface which lie along a first arc in a firstscan plane, the first arc having a radius approximating a radius of theradiused surface; while the array is in the first position, electricallypulsing respective groups of transducer elements of the array insequence using time delays in accordance with a first set of focal laws,which pulsing causes each pulsed group to emit a respective focused beamdirected at the first target location at a respective different steeringangle; applying time delays in accordance with a second set of focallaws to form respective return signals from electrical signals output bythe respective groups of transducer elements in response to echoes fromthe first target location following emission of the focused beamsdirected at the first target location; and selecting a first returnsignal having a first characteristic which indicates it corresponds toan emitted beam that was normal or nearly normal to the radiused surfaceat the first target location.
 13. The method as recited in claim 12,wherein the first characteristic is an amplitude greater than amplitudesof other return signals returned from the first target location.
 14. Themethod as recited in claim 13, further comprising displaying a firstpixel having a first pixel value which is a function of at least thefirst characteristic.
 15. The method as recited in claim 12, furthercomprising: while the array is in the first position, electricallypulsing respective groups of transducer elements of the array insequence using time delays in accordance with a third set of focal laws,which pulsing causes each pulsed group to emit a respective focused beamdirected at the second target location at a respective differentsteering angle; applying time delays in accordance with a fourth set offocal laws to form respective return signals from electrical signalsoutput by the respective groups of transducer elements in response toechoes from the second target location following emission of the focusedbeams directed at the second target location; and selecting a secondreturn signal having a second characteristic which indicates itcorresponds to an emitted beam that was normal or nearly normal to theradiused surface at the second target location.
 16. The method asrecited in claim 15, further comprising displaying first and secondpixels in one column, wherein the first pixel has a first pixel valuewhich is a function of at least the first characteristic, and the secondpixel has a value which is a function of at least the secondcharacteristic.
 17. The method as recited in claim 15, furthercomprising: moving the array from the first position to a secondposition along the axis with an orientation that allows the array, whenproperly phased, to project focused beams which are respectively normalor nearly normal to third and fourth target locations on the radiusedsurface which lie along a second arc in a second scan plane, the secondarc having a radius equal to the radius of the first arc; while thearray is in the second position, electrically pulsing respective groupsof transducer elements of the array in sequence using time delays inaccordance with the first set of focal laws, which pulsing causes eachpulsed group to emit a respective focused beam directed at the thirdtarget location at a respective different steering angle; applying timedelays in accordance with the second set of focal laws to formrespective return signals from electrical signals output by therespective groups of transducer elements in response to echoes from thethird target location following emission of the focused beams directedat the third target location; and selecting a third return signal havinga third characteristic which indicates it corresponds to an emitted beamthat was normal or nearly normal to the radiused surface at the thirdtarget location.
 18. The method as recited in claim 17, furthercomprising displaying first and second pixels in one column in differentrows and a third pixel in a different column in the same row with thefirst pixel, wherein the first pixel has a first pixel value which is afunction of at least the first characteristic, the second pixel has avalue which is a function of at least the second characteristic, and thethird pixel has a value which is a function of at least the thirdcharacteristic.
 19. An ultrasonic inspection system comprising: an arrayof ultrasonic transducer elements; a pulser/receiver unit capable ofsending transmit signals to and receiving return signals from the array;and a computer system programmed with data acquisition software forcontrolling the pulser/receiver unit to form transmit and receive beamsand further programmed with data analysis software for selecting a bestreceive beam returned from a target location on a radiused surface of apart having a curved concave profile, wherein the computer system iscapable of operating in accordance with the data acquisition software tocontrol the pulser/receiver unit to perform the following operations;pulsing the ultrasonic transducer elements in accordance with firstfocal laws calculated to interrogate a first target location on theradiused surface by transmitting a first sequence of focused and steeredultrasonic beams that are directed toward the first target location atdifferent steering angles; forming a first sequence of return signalsrepresenting respective receive beams returned to the ultrasonictransducer elements from the first target location followingtransmission of each focused and steered ultrasonic beam of the firstsequence of focused and steered ultrasonic beams; pulsing the ultrasonictransducer elements in accordance with second focal laws calculated tointerrogate a second target location on the radiused surface bytransmitting a second sequence of focused and steered ultrasonic beamsthat are directed toward the first target location at different steeringangles, wherein the first and second target locations are located alongan arc having a radius equal to an estimated radius of the radiusedsurface; and forming a second sequence of return signals representingrespective receive beams returned to the ultrasonic transducer elementsfrom the second target location following transmission of each focusedand steered ultrasonic beam of the second sequence of focused andsteered ultrasonic beams, and wherein the computer system is capable ofoperating in accordance with the data analysis software to perform thefollowing operations; processing the first sequence of return signals toderive a first set of respective values of a parameter characterizingeach receive beam; processing the second sequence of return signals toderive a second set of respective values of the parameter; selecting oneof the parameter values of the first set that satisfies a condition; andselecting one of the parameter values of the second set that satisfiesthe condition.
 20. The system as recited in claim 19, wherein theparameter values are amplitudes and the condition is having a greatestamplitude within a set of parameter values.
 21. The system as recited inclaim 19, further comprising a display monitor coupled to the computersystem, wherein the computer system is further programmed with softwarefor controlling the display monitor to display a first pixel having apixel value which is a function of at least the one selected parametervalue from the first set and a second pixel having a pixel value whichis a function of at least the one selected parameter value from thesecond set.